Drilling with casing can be accomplished in two different ways. In on instance, a drillable casing shoe is mounted on the end of the casing and rotated down the wellbore. The other way is to lock a drilling bottom hole assembly into a profile bushing near the lower end of the casing string. Using the latter method, more complex drilling equipment can be used, such as downhole motors, directional tools, hole openers, logging or measuring while drilling tools and so on. In many instances, the entire interval can be drilled without removal of the bottom hole assembly. If any of the components of the bottom hole assembly fail or wear out, the bottom hole assembly needs to be unlatched and returned to the surface on drill pipe run in to retrieve the assembly. However, when the bottom hole assembly is removed, there is a risk that the well could kick or blow out. The act of pulling out the bottom hole assembly can cause reduced pressure beneath the bottom hole assembly, also called swabbing, which can induce the well to kick. The annulus around the casing can be closed off with standard casing blowout preventers, but presently there exists no equipment to isolate the casing interior against a well kick or a blowout.
The present invention, in one application, provides a variety of solutions that allow the casing interior to be closed off at least once during removal of the bottom hole assembly. In one embodiment, an internal packer can be triggered on removal of the bottom hole assembly. This packer can be actuated in a variety of ways such as hydrostatically or through a release of gas due to a reaction. Alternatively, a flapper valve can be installed in the casing and held open until removal of the bottom hole assembly at which time a spring can urge it to a closed position to prevent a blowout. Multiple assemblies are contemplated to allow the bottom hole assembly to be removed more than once and still get the blowout protection each time. Upon return of the bottom hole assembly into the casing, the previously set packer can be drilled out or, if a flapper has been used and sprung, then the bottom hole assembly can be simply pushed out of the way.
Other applications of the closure device of the present invention are contemplated. Some of these applications are to control fluid loss during sidetracking, fracturing, and gravel packing. Another application is during perforating to allow the spent gun to be removed with control of the well using the invention in combination with surface blowout prevention equipment. Yet other applications are contemplated to allow a second closure device in the well during a variety of operations to provide control of the well and to meet the requirements of local regulations for redundant closure devices in the event of a blowout.
These and other advantages of the present invention will be more readily appreciated by those skilled in the art from a review of the description of the preferred and other embodiments, the drawings and the claims, all of which appear below.